The fabrication of a semiconductor device involves a plurality of discrete and complex processes. In the fabrication of certain devices, such as but not limited to magnetic RAM (MRAM), one or more metal deposition processes may be performed. The metal may be applied in various ways, such as through sputtering. In a sputtering process, a sputtering target is disposed in a chamber with the substrate. The metal sputtering target is then energized, such as by energetic electrons or ions. Atoms separate from the metal target and are deposited on a substrate. This metal sputtering target may be any suitable metal including, but not limited to platinum, iridium, rhodium, palladium and others.
Ideally, the metal atoms are deposited on the desired regions of the substrate. However, often, some metal atoms become deposited on unintended or undesirable surfaces For example, a MRAM cell includes a magnetic tunnel junction (MTJ). This MTJ is in the form of a stack and comprises a metallic pinned layer and a metallic free layer, and has a thin barrier layer of an electrically insulating material disposed therebetween. If the sidewalls of this stack become coated with metal atoms from the sputtering process, the pinned layer and the free layer may electrically short together, destroying the MTJ.
To prevent this, the metal deposited on the unintended surfaces, such as the sidewalls of the MTJ stack, is removed. This may be done using an etching process. However, in some embodiments, it is difficult to control the etching process, and specifically, the etching rate. Thus, the amount of metal removed from the MTJ stack cannot be readily controllable.
Furthermore, in some embodiments, these metal atoms may be difficult to exhaust from the chamber. For example, platinum is a heavy metal, which easily redeposits on the surface of the substrate during the sputtering etch process and is therefore difficult to remove from the substrate.
Therefore, it would be advantageous if there were a system and method for removing metal from a substrate in a controlled manner. Furthermore, it would be beneficial if the metal that was being removing forms a volatile compound that can be readily exhausted away from the substrate